Telephone system



g 1 1-932 .1. E. O STLlNE 1,871,079

TELEPHONE SYSTEM Filed Aug 28, 1928 www Patented Aug. 9, 1932 seinePATENT JOHN ELLIS OSTLINE, OF LIVERPOOL, ENGLAND, ASSIGNOR TO ASSOCIATEDTELEPHONE AN I) TELEGRAPH COMPANY, OF KANSAS CITY, MISSOURI, ACORPORATION OF DELA- WARE V I TELEPHONE SYSTEM Application filed August28, 1928, Serial No. 302,613, and in Great Britain September 5, 1927.

The present invention relates to telephone systems and is moreparticularly concerned with arrangements for giving tones to callingparties to indicate the progress of a connection. Such tones aresometimes employed in manual systems but in automatic systems theybecome almost essential in view of the fact that there is no operator toinform the calling party how the call is progressing. It has usuallybeen considered desirable in automatic systems to give a calling partywhat is known as a ringing tone which may be described as an echo of theringing of the wanted partys bell, from which the calling party gathersthat the connection has been properly set up and that if he receives noreply it is because the wanted party has not answered. The-simplestmethod of supplying this tone is to allow some of the actual ringingcurrent to leak back through a small condenser in the direction of thecalling partys station, and this arrangement is found quite satisfactorywhen ringing generators are employed of the pole-changer type which givea wave with very sharp peaks and hence a considerable proportion ofhigher harmonics. In case, however, a rotary alternator giving a closeapproximation to a sine wave is made use of, it is found that the amountof ringing current of suitable frequency which leaks back through theringing tone condenser is not sufficient to give the calling party there quired audible indication. One method of overcoming this difficultywhich has been employed is to superimpose on the ringing current a toneobtained from an independent tone source; for instance the lead from thegenerator may pass through the secondary of a transformer, the primaryof which is connected to a high-speed interrupt-er. In this case it isclear that the calling party will receive ringing tone in exactcorrespondence with the ringing of the wanted partys bell.

It has been found however that the tone obtained by this means issubject to considerable variation in volume in accordance with the loadon the generator and that when this load is very heavy the ringing toneobtained is almost inaudible and therefore unsatisfactory. The presentinvention aims at overcoming this dificulty sothat a tone of constantvolume is obtained irrespectiveof the number of bells which are beingsupplied from the ringing generator at any particular instant.

According to the invention this is effected by arranging that theringing current and ringing tone are obtained from separate to theconnector; since as already pointed out,

the'ringing current itself, when a pure sine wave, is inaudible to acalling party this will occasion nodifliculty.

The invention will be appreciated from V the following description ofone method of carrying it into efiect which should be taken inconjunctionwith the accompanying drawing. This arrangement is designedfor a system in which ringingcurrent is' supplied intermittently forperiods of equallength separated by alternate long and short pauses.This arrangement while possessing other advantages permits a ringingtone corresponding exactly thereto to be readily difi'erentiated fromother tones such as busy tone, which in addition to being of differentpitch is applied in pulses which alternate with silent intervals of thesame length. It will be apparent therefore that if the ring-back tonewere applied for the whole time that ringing current was not beingapplied, the

tone received by-the calling party would not correspond exactly with theactual ringing conditions. In the arrangement shown, therefore, twointerrupters are employed, forin' stance with the phase relationshipshown,

which are mounted on the same shaft and thus rotate together. The lead Lis a common lead extending to a group'of connector switches or cordcircuits if ringing current is to be supplied to a manual operatorsposition. In the position of the cams C1, 02 shown, this lead L isconnected to earth and neither tone nor ringing current is thereforebeing fed out. As the cams rotate in the two will never be appliedtogether." In'the arrangementshown the tone is obtained from the highspeed interrupter I but clearlyany other suitable tone generator maybe'employed. Furthermore itwouldalso be possible to operate both setsofinterrupter springs from a single cam,-the springs then e-beinglocated substantially 180 apart to produce the same effect as thearrangement shown;

I claim 1. Ina telephone system, a source of'ringaging current and asource of ringing-tone,-two

cam-controlled interruptersprings, a conductor connected to the first ofsaid springs, a front-contact for said first spring for=connecting saidconductor tosaidringing-cur- 5.2:rent source, a back contact for saidfirstspring forextending-said conductorto said-second spring, a'frontcontac-t forsaid second spring for connecting saidconductortosaidringingtone source, and a back contact for said sec-,1ond;spring for grounding:v said conductorwhen disconnected frombothof'said sources.

.2. Ina'telephone system, a conductor a' source of ringingcurrent and asource of: ringing tone, means for connecting said ring-" aingcurrentsource to said conductor at inter vals-to pro-du'cea ringingsignal'atthecalledstation followed by arelatively long. silent period,--saidringin-gsignal being inaudible to the calhnglsubscriber, and means forcon-- xnectingsald ringing tone source to said 0011- ductor at likeintervals duringisaid silent periods to provide a ringback-tone for: thecall= ing subscriber which simulates said ringing signah 3.-- Inatelephone system, a conductor, a generator for generating ringing.current having substantially a sine curvexwave 'formwhich will not leakback through a small con denser and is therefore inaudible to acallingsubscriber, a-source ofringing tone, a camcontrolled interrupter springfor connecting: said generator to said conductor at intervals source ofringing current and a source of ringing tone, means for connecting saidringmg current source to said conductor at definite periods inaccordance with a predeter mined code, there being a relatively longsilent-period between the end ofv one code signal and the beginning ofthe next code signal, and means for connecting said ringing tone sourceto said conductor in accordance with SilldCO'dQ duringSalClSlleIltPQFlOfl'tO' provide a code tone signal for the" callingsubscriber which slmulates said code'rlnging signal.

In testimony whereof I have signed my name at Liverpool, England, this14th day of Au'gust'21928.

JOHN ELLIS OSTLINE.

to produce a ringingsignal followed by a relatively long silent period,and asecond cam-controlled interrupter spring-for connectin-g saidringing tone source tosaid conductor at like intervalsdurin'g saidsilent' periods to provide a ringback tone which simulates'saidringing-signal.-

45. In a telephone system, a conductorpa

